With the shrink of the critical dimensions of the future generation of semi-conductor devices, the introduction of new materials, especially having high dielectric constant, is required. In CMOS architectures, high-k dielectrics are required to replace SiO2 which reaches its physical limits, having typically a SiO2 equivalent thickness of about 1 nm.
Similarly, high-k dielectrics are required in Metal-Insulator-Metal architectures for RAM applications. Various metal compositions have been considered to fulfill both the materials requirements (dielectric constant, leakage current, crystallisation temperature, charge trapping) and the integration requirements (thermal stability at the interface, dry etching feasibility . . . ).
The Group IV based materials, such as HfO2, HfSiO4, ZrO2, ZrSiO4, HfZrO4, HfLnOx (Ln being selected from the group comprising scandium, yttrium and rare-earth elements) are among most promising materials. Furthermore, Group IV metals composition can also be considered for electrode and/or Cu diffusion barrier applications, such as TiN for mid-gap metal gate and MIM RAM, HfN, ZrN, HfSi, ZrSi, HfSiN, ZrSiN, TiSiN . . . .
Deposition processes of such thin films with reasonable throughput and acceptable purity are vapor phase deposition techniques, such as MOCVD (Metal-organic Chemical Vapor Deposition) or ALD (Atomic Layer Deposition). Such deposition processes require metal precursors that must fulfill drastic requirements for a proper industrial use.
It is known from Kim et al., Electrochem Soc Proceedings 2005-05, 397, 2005, to use HfCl4 for the deposition of HfO2 by ALD. However, some by-products generated during the deposition process, such as HCl or Cl2, can cause surface/interface roughness that can be detrimental to the final properties. Other possible byproducts, depending on the oxygen source used, may be hazardous. For instance, OCl2, through the OCl fragment by QMS, has been detected as a byproduct of the reaction between HfCl4 and O3. Moreover, in the case of high-k oxide, Cl or F impurities are detrimental to the final electrical properties and Cl and F-containing precursors are therefore not preferred.
Triyoso et al. in J. Electrochem. Soc. 152 (3) G203-G209 (2005), Chang et al. in Electrochem. Solid. State Let., 7 (6) F42-F44 (2004), studied the use of Hf(OtBu)4 for HfO2 MOCVD and ALD, respectively. Williams et al. have evaluated Hf(mmp)4 and Hf(OtBu)2(mmp)2 for MOCVD of HfO2. In WO2003035926, Jones et al. disclose solid Ti, Hf, Zr and La precursors improved with donor functionalized alkoxy ligand (1-methoxy-2-methyl-2-propanolate[OCMe2CH2OMe, mmp]) which helps inhibiting oligomerisation of Zr and Hf alkoxide compounds and increasing their stability towards moisture. However, all those alkoxide precursors have the drawback not to enable self-limited deposition in ALD process.
Alkylamides precursors such as Hf(NEtMe)4, Hf(NMe2)4, Hf(NEt2)4 . . . have been widely disclosed in the literature such as by Senzaki et al in J. Vac. Sci. Technol. A 22(4) July/August 2004, Haussmann et al. in Chem. Mater. 2002, 14, 4350-4353, Kawahara et al. in J. Appl. Phys., Vol 43, No. 7A, 2004, pp 4129-4134, Hideaki et al. in JP2002093804, Metzner et al. in U.S. Pat. No. 6,858,547, Dip et al. in US20050056219. Group IV alkylamides are both suitable for ALD and MOCVD processes. Furthermore, some are liquid at room temperature (TDEAH and TEMAH) and of sufficient volatility, and they allow self-limited ALD at low temperature for a limited thermal budget process. However, Group IV alkylamides have several drawbacks:                they may decompose during the distribution to some extent leading to a possible clogging of the feeding line or the vaporizer,        they may generate particles during deposition,        they may entail non-uniform compositions during deep trenches deposition processes,        they only allow a narrow self-limited ALD temperature window, hence reducing the process window.        
Carta et al. disclose in Electrochem Soc Proceedings, 260, 2005-09, 2005 the use of bis(cyclopentadienyl)bisdimethyl hafnium and several authors (Codato et al., Chem Vapor Deposition, 159, 5, 1995; Putkonen et al., J Mater Chem, 3141, 11, 2001; Niinisto et al., Langmuir, 7321, 21, 2005) disclose the use of bis(cyclopentadienyl)bisdimethyl zirconium, which allow an efficient ALD deposition process with an ALD window up to 400° C. and an achievement of films with less than 0.2% C in optimized conditions with H2O as co-reactant. However, HfCp2Me2 and ZrCp2Me2 both have the drawback of being solid products at room temperature (HfCp2Me2 melting point is 57.5° C.). This makes inconvenient their use by IC makers.
In U.S. Pat. No. 6,743,473, Parkhe et al. disclose the use of (Cp(R)n)xMHy-x, to make a metal and/or a metal nitride layer, where M is selected from tantalum, vanadium, niobium and hafnium, Cp is cyclopentadienyl, R is an organic group. Only examples of tantalum and niobium cyclopentadienyl compounds are disclosed. However, no liquid precursor or a precursor having a melting point lower than 50° C. is disclosed.
Today, there is a need for providing liquid or low melting point (<50° C.) group IV precursor compounds, and in particular Hf and Zr compounds, that would allow simultaneously:                proper distribution (physical state, thermal stability at distribution temperatures),        wide self-limited ALD window,        deposition of pure films either by ALD or MOCVD.        